Electrical and electronic parts mounted on a vehicle have been conventionally designed in compliance to a battery voltage of 12 V. However, a voltage of a battery for the vehicle is increased to a high voltage of 42 V in recent days. Accordingly, an electric current flowing therethrough is widely increased and a generated electric power is increased in the case of employing the conventional design, so that a problem is caused. In the case of a heating element for a door mirror heater or the like, if the heating element of the specification of 12 V is used under 42 V, an initial power becomes 12.25 times (on the basis of the expression P=I·E). Further, since a resistance is not infinitely great even in a PTC heating element, there is a risk that the temperature exceeds a set temperature range.
In the door mirror heater for the battery voltage of 12 V, an initial resistance value is set to be less than 2 to 20 Ω on the basis of the required heat generation temperature. However, in the case that the door mirror heater is attached to the vehicle mounting the high voltage battery having the voltage of 42 V as it is, the initial current value is increased, and exceeds a current distribution with respect to the other electrical equipments on the basis of the battery capacity, and the heat generating amount becomes enormous. Accordingly, even if the PTC function is provided, the heat generation temperature exceeds the set range (refer to Japanese Unexamined Patent Publication No. 2001-284859, Japanese Unexamined Patent Publication No. 2002-50456, Japanese Unexamined Patent Publication No. 2002-146251 and the like).
The present invention is made by taking the points mentioned above into consideration, and an object of the present invention is to provide a door mirror heater which can corresponds to a high voltage battery.